1. Field of the Invention
The present invention relates generally to robotic welding, and more specifically to torch alignment verification to assure quality welds in an automated welding process.
2. Related Art
Robotic welding techniques require relatively precise location of the welding torch relative to a workpiece. Typically a welding wire is fed through a welding tube, and any misalignment of the wire tip with respect to the workpiece can result in an inferior weld. If the wire tip is offset more than a very small fraction of an inch from the desired location in the path, the resulting weld can be uneven and weak since weld leg length and/or penetration are adversely affected by the offset. There are numerous sources of torch and wire tip misalignment (including non-rigid torch mounts, multiple articulation points on the robot arm, and deflection caused by heat in the welding tube itself), and less than optimum welds caused by torch and/or tip misalignment are not uncommon.
Several approaches have been utilized to deal with the problem of misalignment, but most of these have been relatively time-consuming or expensive or have not provided an accurate indication of wire tip alignment. One method in use involves clamping the robot wrist to a fixture and then determining if the tip is at a preselected location relative to the fixture. This and similar types of clamping methods are time-consuming and can usually detect only torch position variations resulting from problems arising between the clamped area and the tip. Variations caused by a problem elsewhere in the system may go undetected. Other methods, such as touch sensing utilizing a voltage source and contacting a specific area at the workstation, do not provide an indication of tip location which is sufficiently accurate to avoid poor welds due to wire tip misalignment.